1. Technical Field
The present invention relates to a printing apparatus that forms an image by relatively moving a carriage along a target printing surface of a printing medium.
2. Related Art
Ink jet type printing apparatuses are well-known as a representative example of this type of printing apparatus. In these types of printing apparatus, ink droplets are discharged onto a surface of a printing medium while moving in a transport direction of a printing medium, a main scanning direction that intersects a so-called sub-scanning direction, in a state in which a carriage that is mounted with a printing means becomes separated from a surface of the printing medium (target printing surface) from above, and the printing medium is sequentially transported in the sub-scanning direction. In this manner, an image is printed on the printing medium.
In this type of printing apparatus, there are cases in which creases in a printing medium, which are caused by shifts in transport during the transport of the printing medium, occur. In addition, there are cases in which waves, so-called cockling, are generated in the printing medium by stretching and the like that results from ink absorption and the temperature and humidity of the printing medium. If this phenomenon occurs, the printing medium is partially lifted up, and there are cases in which the carriage rubs against or impacts with the surface of the printing medium during a printing operation.
In order to deal with this problem, a technology which is provided with a sensor that detects uplift of the printing medium in the vicinity of the carriage, and in which movement of the carriage is stopped when uplift is detected, has been considered. For example, in JP-A-5-262019, a technology in which changes in a gap between a recording head and a target recording material are detected by an optical detection type sensor, and the movement of the recording head is stopped in cases in which the amount of change differs from a defined amount, is disclosed.
The configuration of the optical detection type sensor is not specifically disclosed in JP-A-5-262019, but for example, the optical detection type sensor that is disclosed in JP-A-2006-168138 is an example of technology that can be used for such an application. In the technology that is disclosed in JP-A-2006-168138, light is caused to be incident to a target recording medium from an oblique direction, and the surface height of the target recording medium is determined by detecting the position at which specular reflected light from the target recording medium is the strongest.
In a configuration in which the height directional positioning of a printing medium is detected optically in this manner, there are causes of false detections such as the direction of specular reflected light changing as a result of inclinations in the surface of the printing medium that occur due to uplift thereof, or detection not being performed for transparent printing media which causes light to pass through. Therefore, there is a concern that it may be possible to completely avoid impacts between the carriage and the printing medium due to the false detection of positions, and that the action of the apparatus may be stopped even though there is a state in which impacts have not occurred.